Daphnia

Daphnia are filter feeders, continuously straining water to collect unicellular green algae, bacteria, yeast, and fine organic particles. They can be fed green water (phytoplankton), brewer's yeast suspended in water, spirulina powder, or commercial microalgae solutions. Overfeeding must be avoided as uneaten organic matter quickly fouls the water and crashes the culture.

Daphnia are completely peaceful and pose no threat to any tank inhabitants; they exist solely as prey and filtration organisms. They exhibit a characteristic jerky, pulsing swimming motion throughout the water column, driven by their large antennae. In culture tanks they form dense clouds and are highly sensitive to copper, chlorine, and most medications, making them unsuitable for medicated display tanks.

Daphnia are one of the easiest live foods to culture. In good conditions females reproduce without males, releasing a brood of all-female young every few days, so a culture grows quickly. When crowded, too warm or kept in poor water, they switch to resting eggs called ephippia, which survive drying out and hatch when conditions improve.